<h2>DESCRIPTION</h2>

This module creates an output raster map centered on the <em>x,y</em> values specified
with the <em>coordinate</em> parameter, out to the edge of the current region.
The output cell values increase linearly from the specified center. The <em>min</em> 
and <em>max</em> parameters control the inner and outer output raster map radii, respectively. 

<p>The <em>mult</em> parameter can be used to multiply the output raster cells by a common factor.
Note that this parameter does not affect the output raster position or size; only the z-values
are changed with this parameter. 
<p>Binary-output raster maps (solid circles of one value) can be created
with the <b>-b</b> flag. Raster maps so created can be used to create
binary filters for use in <em>i.ifft</em> (inverse Fourier transformations;
apply filter with <em>r.mask</em>).


<h2>EXAMPLES</h2>

Generate a raster circle at current map center with a radius of 300m and outwardly
increasing raster values:

<div class="code"><pre>
EASTCENTER=`g.region -c |  awk ' /center easting:/ { print $3 }'`
NORTHCENTER=`g.region -c | awk ' /center northing:/ { print $3 }'`
r.circle output=circle coordinate=${EASTCENTER},${NORTHCENTER} max=300
</pre></div>

Generate a binary raster ring around current map center with an inner radius 
of 500m and an outer radius of 1000m:

<div class="code"><pre>
EASTCENTER=`g.region -c |  awk ' /center easting:/ { print $3 }'`
NORTHCENTER=`g.region -c | awk ' /center northing:/ { print $3 }'`
r.circle -b output=circle coordinate=${EASTCENTER},${NORTHCENTER} min=500 max=1000
</pre></div>


<h2>SEE ALSO</h2>
<em>
<a href="g.region.html">g.region</a>,
<a href="g.remove.html">g.remove</a>, 
<a href="g.rename.html">g.rename</a>, 
<a href="i.fft.html">i.fft</a>, 
<a href="i.ifft.html">i.ifft</a>,
<a href="r.mask.html">r.mask</a>
</em>


<h2>AUTHOR</h2>
Bill Brown, U.S. Army Construction Engineering Research Laboratory<br>
Additional flag/min/max parameter by Markus Neteler, University of Hannover

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